Long-Range Channel Prediction for Adaptive OFDM Systems I. C. Wong, A. Forenza, R. W. Heath and B. L. Evans April 21, 2019

Adaptive OFDM Adapt modulation, coding, or power in each subcarrier at the Transmitter (Tx) in order to maximize throughput Adaptation based on current channel state information (CSI) being fed back to the Tx Problem: Outdated CSI [Souryal & Pickholtz, 2001] Effect very relevant in mobile situations How do I minimize the impact of this delay? April 21, 2019

Wireless Channel Prediction Long-range prediction (LRP) [Duel-Hallen, et. al. 2000] Used an FIR Weiner prediction filter Designed for flat-fading channels Key Idea: Downsampling the observed channel coefficients April 21, 2019

Application of LRP to OFDM Briefly investigated in [Forenza & Heath, 2002] Directly predict channel for each of the N subcarriers Valid since each subcarrier is a flat-fading narrowband subchannel Storage needed for p*N previous channel coefficients ck and p*N prediction coefficients dk Used Burg’s algorithm to compute predictor coefficients April 21, 2019

Low-Complexity LRP for OFDM Pilot-tone Prediction Perform LRP on the Npilot pilot tones only Since Npilot < N, less computation and storage needed (e.g. Npilot = 8; N = 256 for 802.16e ) Use the same Wiener predictor for the subcarriers nearest to the pilot carrier Pilot … … Data Carriers April 21, 2019

Low-Complexity LRP for OFDM Time Domain channel tap Prediction Perform LRP on the L ≤ Npilot time domain channel taps, and thus further reduce complexity It can be shown that MMSE predictor for the time domain taps also minimize MSE for frequency domain … t=n t=1 t=0 April 21, 2019

Simulation Parameters (IEEE 802.16e) Value N 256 BW 5 MHz Guard Carriers (7) [0-27] & [201:256] Fcarrier 2600 MHz Channel Model ETSI Vehicular A Mobile Velocity 75 kph Prediction Order 75 Downsampling rate 25 (4*fd) April 21, 2019

Channel Prediction Example April 21, 2019

Performance comparisons April 21, 2019

Conclusion LRP for OFDM systems can be accomplished by: Prediction on all the tones Prediction on pilot tones Prediction on the time domain channel taps Time-domain prediction gives better MSE performance, specially in the presence of channel estimation error Future work: Adaptive prediction with Weiner smoothing April 21, 2019